The electrical and optical properties of the In-rich InAlN alloys are strongly influenced by native point defects. Here the effects of the defects are studied using 2 MeV He+ irradiation to vary the defect concentration. Localized native defects in In1−xAlxN(x < 0.45) are predominantly donors, with energy levels located above the conduction band edge. Accordingly, the electron concentration increases and the optical absorption edge blue shifts with increasing irradiation fluence before saturating at high fluences. Saturation occurs when the Fermi level reaches the Fermi level stabilization energy, which is the average energy of localized native defects in semiconductors, at 4.9 eV below the vacuum level. The energy position of the native defects also explains the initial increase followed by the quenching of the photoluminescence (PL) intensity, as well as the blue shift in the PL peak, with increasing irradiation fluence.